1. Field of the Invention
This invention relates generally to concrete finishing machines, and, more particularly, to apparatus for controllably adjusting the pitch of the trowel blades of such machines.
2. Background Information
Concrete finishing machines have been used for many years to level and finish large concrete pads. Such machines typically include a rotatable trowel blade assembly having a plurality (e.g., three or four) of generally planar trowel blades mounted on trowel arms projecting radially outwardly from a common hub, all of which are rotated by a gasoline-powered engine. The trowel blades rest directly on the concrete surface to be finished and support the machine's entire weight.
Concrete finishing machines typically further include means for controllably pivoting the trowel blades about their respective radial axes, to change their pitch relative to the concrete surface to be finished. Changing the blades' pitch correspondingly changes the proportion of blade surface contacting the concrete surface, such that the machine's weight is supported by a larger or smaller area of the surface.
In use, the machine makes several passes over the concrete surface as the concrete hardens, with the blade pitch being specially selected for each pass. In the initial pass, when the concrete is still very wet and plastic, the blade pitch is usually adjusted to be substantially parallel with the concrete surface, thereby lying flat upon it and spreading the machine's weight over a maximum surface area. In subsequent passes, as the concrete hardens and becomes less plastic, the blade pitch is progressively increased, with the pitch used in the final pass sometimes being as much as about 30 degrees.
Improvements in recent concrete formulations have made some concrete slabs include pockets or areas of varying plasticity. In such situations, it is necessary to rapidly adjust the trowel blade pitch in order to produce the desired finish. It is also necessary to adjust the trowel blade pitch when the machine is being moved to an adjacent area where the concrete is at a different stage of hardness. In this situation, which frequently occurs when very large concrete pads are being formed, the blade pitch must be adjusted very rapidly.
In the past, the pitch of the trowel blades was typically adjusted using a thrust collar that pushed downwardly on fingers projecting upwardly from the rear sides of the respective trowel arms. Typically, such a downward force on the thrust collar is provided by a yoke or fork that is pivotally secured to the machine's frame and connected to an actuator means adjacent the device's handlebars. By operating the actuator means, the pitch yoke is manipulated thereby applying (or removing) a force on the thrust collar. Examples of such a yoke and thrust collar pitch control can be seen in U.S. Pat. Nos. 3,412,657 (Colizza et al.), U.S. Pat. No. 3,791,754 (Zochil), U.S. Pat. No. 4,232,980 (Tertinek et al.), U.S. Pat. No. 4,577,993 (Allen et al.), U.S. Pat. No. 4,673,311 (Whiteman, Jr.), and U.S. Pat. No. 5,405,216 (Allen et al.).
A disadvantage to this use of yoke (or fork) is the fact that the thrust collar is depressed (or lifted) at two points, namely by its contact with the ends of the two arms of the yoke. Having pressure applied at two points can lead to slight tilting of the thrust collar and thereby resulting in wear between the thrust collar and the drive shaft and/or the thrust collar wear bushing inserted between the drive shaft and the thrust collar. What is needed is a method of moving a thrust collar that eliminates this wear caused be the application of pressure by a yoke.
A second disadvantage with a yoke and thrust collar system is the necessity to use cables, chains and other means of moving the yoke. In order to conceal and protect these means, they typically extend from the handlebars to pitch controller via the inside of the handle. Because of this, such a handle is limited in minimum diameter and is unable to be foldable. What is needed is the ability to fold the handle.
A third disadvantage to the prior art yoke and thrust collar system is the fact that the user must physically supply the force necessary to move the thrust collar into engagement with the fingers of the arms of the blades. Various mechanical means are shown in the prior art which help reduce the amount of force required, but the fact remains that the user is still required to physically depress or lift the thrust collar. What is needed is a pitch controller that does not require the user to physically manipulate the thrust collar.
A fourth disadvantage to many renditions of the old yoke system is the convenience of the user. The trailing edge of each trowel blade, which contacts the concrete surface on which the machine rests, is spaced from the blade's pivot axis. Any change in blade pitch therefore transfers the machine's weight by raising or lowering the machine on the surface. Since the machine is generally quite heavy, usually weighing several hundred pounds, the screw handle used for blade pitch adjustment must have threads with a very small pitch to permit the operator to rotate it conveniently. Consequently, the blade pitch adjustment can be made only very slowly. This has been proven to be unsatisfactory in many situations. Some concrete finishing machines have overcome the slow pitch adjustment afforded by the screw handle described above by replacing the screw handle with a long lever attached to the machine's framework. Although this configuration permits a rapid adjustment of the blade pitch, it is not generally convenient to use. This is because the lever requires large movements for lever advantage and because the lever is not conveniently located on the machine handle itself and thus requires the operator to control the machine using merely one hand and unsteady footing. What is needed is a means of changing pitch which requires less digital manipulation than the prior art methods.
It should be appreciated from the foregoing that there is a significant need for a concrete finishing machine having a trowel blade adjustment apparatus that can be used by the operator to mechanically adjust the trowel blade pitch, yet is simple in construction and convenient to use. The present invention fulfills this need.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.